The present invention pertains to self-drilling connecting unit with a plate-shaped cutting tool attaching to a shaft.
The use of plate-shaped cutting tools is known both for drills and also for self-drilling connecting units. The use of plate-shaped cutting tools is better than of circular cross section drills, because the drilling power is much better and because the drilling performance can be adapted to the particular job.
Patent AT-PS 356 462 discloses how to provide a central, longitudinal slit at the free end of the shaft of a screw, in this slit a cutting plate is installed. Now elevations and/or depressions are provided on the cutting plate for shape- and/or force-fit insertion into the longitudinal slit of the screw. Moreover, on the cutting plate some ribs are provided and they run parallel to the central axis on the region turned away from the cutting. These ribs are set in parallel rows and are located on both facing surfaces. These ribs are of cutter-like design and have a triangular cross section for this purpose. Merely the placement of these cutter-like ribs will ensure a fixed mount of the cutter plate in the longitudinal slit, which makes an additional gluing superfluous. Naturally for particularly severe uses, an additional gluing or other connection is possible, and the provided ribs then make possible a preliminary fixing in place and thus an easier handling. This known, self-drilling screw thus requires a complicated cutting plate, but this does not ensure that it will be properly centered and aligned with respect to the shaft during the mounting.
From DE-OS 25 49 147 it is known how to form a slit on the free end of a self-drilling screw with circular cross section and drill bit equipped additionally with grooves and cuts. A platelet-like cutting tool is inserted into the slit and is joined in an additional work step with the drilling unit by welding, soldering or gluing. Here too, it is not possible to center the platelet-like cutter during the mounting, and in addition, in any case one work step is required to establish a secure link between cutting tool and drilling unit.
From DE-OS 25 55 647 a drilling screw is known whose shaft has a drilled hole on the end opposite the screw head. The drill point of the screw is a separately produced joining piece that has a mounting shaft that extends into the drill hole of the shaft and is attached therein by soldering or gluing. But the mounting shaft can also be designed as a slender cone and pressed into the hollow-conical drill hole of the screw. In this known drill screw it is of course possible to center the unit when mounting the drill point; but the production of the drill point is complicated since it is composed of a platelet-like part to which the cylindrical or conical-shaped mounting shaft is attached or mounted.
From U.S. Pat. No. 22 66 892 an anchoring device is known that consists of a bolt provided on one end with a thread and on the other end with a forged, arrowhead-like head. Instead of this, the shaft can also be provided with an axial slit, in which a platelet-like head unit, to be produced separately, can be attached by welding, riveting or similar means. It is not possible to center the unit described in this patent.
U.S. Pat. Nos. 37 15 952 and 37 18 067 describe an expansion anchor unit or a mounting system where a platelet-like cutting tool is installed in an axial slit at the end of a shaft and is held form-fitted therein for hole drilling. After drilling the hole and removal of the shaft, another shaft-like part is driven into the hole, expanded by the platelet-like cutter remaining in the in drill hole, and thereby attached in the hole. Now it may be possible to center the unit here, but the platelet-like cutting tool will only be held loosely in the axial slit since the shaft after drilling, is to be pulled from the drilled hole without the cutting tool.
Finally, from AT-PS 232 908 a drill for drilling through rock, hard shingles and similar mineral materials is known that has a cylindrical drill element with a diametrical groove formed on the end. The sections of the drill element extending along the groove are curved around in the opposite directions so that a rear support is created for the parts extending outside the cylindrical perimeter of the drill element of a cutting metal plate installed in the groove. The cutting metal plate is mounted in the groove by hard soldering or similar means. But it is not possible to center the cutting metal plate during its assembly.
Now all the above, known, self-drilling connecting units or drills have a difficult problem of holding the platelet-like cutting unit in the proper position to the shaft until final, secure connection, in order to ensure a proper axial alignment between the platelet-like cutting tool and the shaft.